Back to the point about the toys--
I kind of disagree. The toys are not what the Joker is--they are one of many manifestations of what he is, but they are by no means necessary. The Joker is a JOKE, sure--but I think the expression of that can vary considerably and still feel very Joker.
Here's the thing: Batman and Joker need to be in sync with each other. The zaniness of the Joker depends entirely on how it happens to be playing off Bats. The poisoned cotton candy Joker is in a comic with a hardass, guns-on-the-batomoblie Batman. It's a gritty comic overall, with the Batman/Joker dyanmic working together to present a unified feel of the story.
Nolan's Batman IS a lot less campy, a lot less gimmick happy than prior Batmans--therefore, the Joker has to be less campy and random, or else you run into the whole "MEANWHILE, IN A COMPLETELY DIFFERENT MOVIE," problem, and nobody seems legit.
So given that Nolan's Batman has explanations for everything (training, he doesn't make all his own gear because Lucius is helping, etc), Nolan's Joker is going to have to be grounded in the real world to a certain and significant extent. Movies--stories--ask you to suspend disbelief, sure. But you can't expect the audience to suspend significantly MORE disbelief about one character in the movie, or the tone of the story falls apart and it becomes very tawdry. So we can't have a Batman that gets all of his gear in plausible ways and then a Joker that--ALL OF A SUDDEN! FOR NO GOOD REASON! (thanks, Burton)--has a bunch of mime trained goons and rigged gag toys. I think this Joker is going to be a lot more about working with fairy ordinary things and making them uncomfortable and gruesome, rather than going for bright and cheap and cheesy "TA DA!" moments that would take a hell of a lot of resources to pull off.
And, I mean, compared to a lot of other movies? Batman asks you to suspend a lot LESS in the way of disbelief, because being rich and brilliant and jacked is, well, less of a stretch than being sole surviving uberman from a dead planet who happens to fit right in. I mean, come on.
For me, the Joker's always been a state of mind, and thus the thematic implications of the character all revolved around the psychological. The Joker isn't toys to me; the Joker is emotional dissonance, 'what does sanity mean?' and an exploration of sociopathy. The Joker's all about improper emotional response--things are funny that shouldn't be, jokes meant to be funny aren't, horribly things are funny depending on where you look at them. It's the horror/laughter thing that totally messes with our idea of what's safe, and there's a LOT more to that than surprise gags.
So for me...yeah, acid flowers would be mind trippy. You know what else would be mind trippy? A DIRTY CLOWN STABBING YOU IN THE FRIGGIN' FACE.
You'd have nightmares about that forever if you survived it (which you wouldn't), and feel just as stupid saying it out loud to someone who hadn't been there: "uh--there was this clown, right, this guy in this clown kinda make up, anyway, and he took this knife and--no, really, red smile and everything--OHGODITWASHORRIBLE. DON'TJUDGEME." If anything I think it would be worse to relate afterward than an acid flower...
I don't like some of the toys because I feel they lack finesse. I like my Joker competent, scary, and in love with himself. He COULD take the easy way out--"ooga booga I'm a scary clown with scary clown toys!"--but he doesn't, because he is BETTER than that. He's a clown in a tuxedo dancing the tango with a psychiatrist turned psycho groupie--and she was just a diversion while he was taking some time off. The man is good at what he does--he isn't really a clown, not really. He's the clown PRINCE of crime, which is classier, and a serious opponent for Batman in terms of will and cunning.